1. Field of the Invention
This invention is directed to methods and apparatus for correcting for image data from a medical imaging scan of a subject, into which subject a specified amount of an imaging substance has been introduced, in particular to dose infiltration in PET imaging.
2. Description of the Prior Art
In the medical imaging field, several imaging schemes are known. For example PET (Positron Emission Tomography) is a method for imaging a subject in 3D using an injected radio-active substance which is processed in the body, typically resulting in an image indicating one or more biological functions. Other such functional imaging modalities are known, such as SPECT.
In such functional images, many important pathologies and anatomical structures appear as very high (or low) intensities. For example, a tumour in an FDG-PET image will often appear as a bright region.
When a PET radiotracer is injected into a patient, dose infiltration may occur when not all of the radiotracer is injected into the vein. The maximal intensity projection (100) shown in FIG. 1 illustrates a case with dose infiltration at the injection site (102). The infiltration can be seen as highly increased uptake in the region (104) around the injection site. In this case the maximum SUV at the site of infiltration is more than 4000.
The potential impacts of this on the clinical workflow are as follows:
1. Axial slices in which an infiltration site is present suffer from reduced intensity granularity due to rescale slope and intercept (RSI) encoding in DICOM, in addition to other image artifacts that affect the clinical readability of those slices.
2. Standardized Uptake Values (SUVs) for the entire patient are no longer reliable as the infiltrated dose is not able to circulate around the body, so only a fraction of the injected dose is available for uptake by tissue.
Regarding the first of the potential clinical impacts listed above, if the dose infiltration is detected before the patient leaves imaging facility, the bed position affected by the infiltration site can be rescanned with the infiltration site moved outside the field of view (FOV).
Rescanning the affected bed position will not, however, address the second problem of unreliable SUVs. This can only be addressed by repeating the entire imaging process at a later time, exposing the patient to additional dose from the radiotracer and the CT scan for attenuation correction.
Dose infiltration also affects other imaging modalities (such as MR, or ultrasound) in which imaging substances are introduced to the subject, where not all of the imaging substance is properly introduced, either by injection or insertion, so that the initial amount of the imaging substance is reduced by an unknown proportion.